A transient sodium-hydrogen exchange system induced by catecholamines in erythrocytes of rainbow trout, Salmo gairdneri.

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RESUMO

The addition of isoprenaline to an isotonic suspension of red blood cells of rainbow trout induces an amiloride-sensitive Na+ transport which is independent of Cl- and insensitive to 4,4'-diisothiocyano-2,2'-stilbene disulphonic acid (DIDS) and furosemide. Na+ uptake is accompanied by amiloride-sensitive H+ release. The H+ efflux is dependent upon the external Na+ concentration, the K0.5 value for Na+ being 16 mM. In the presence of DIDS, when the coupled NaCl entry (NaCl co-transport) induced by catecholamine is blocked, the results provide evidence for a linked movement of Na+ and H+, with a stoicheiometry of 1:1. Exchange of H+ for Na+ induces osmotic swelling of the cells which is due to the replacement of a bound proton by an osmotically active Na+ cation. In the absence of DIDS when the bulk of the Na+ uptake is the result of a coupled entry of Na+ and Cl-, H+ extrusion still occurs and the magnitude of acid excretion is identical to that found in DIDS-treated cells. This suggests that Na+-H+ exchange remains active. Addition of isoprenaline first stimulates the Na+-H+ exchange but only transiently. This is followed by a more permanent stimulation of the NaCl co-transport.

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